Hey guys, our bass boat has a 1985 70hp evinrude on it, and we are having a bit a problem with it, wanted to see if anybody could help give us an idea of what it might be.

The motor fires up pretty much every time, but about 70% of the time, when we hit the throttle, it will just barely start to accelerate and then the motor will die, and we'll have to start it back up. We have tried running the idle bar up for a few seconds to try to clean anything thing out, then drop it down, and try to accelerate and occasionally that seems to help, but not usually.

It will run if we very very slowly add throttle, like spend 30 seconds or so getting to full throttle, but if we do it any faster, it usually dies.

Once you get it going, it never dies or anything, its just in that initial attempt to accelerate.

We recently changed the spark plugs, the fuel is fresh, and we are running a 50:1 ratio on fuel to oil (that ration was confirmed by a local shop.)

Anybody have any ideas on what could be the problem?

That is a carb problem. Get a good mechanic to clean the carbs and install carb kits.

Check all the small fuel lines comming off the carbs to see if they are cracked and leaking, I had a simular issue with my old Merc

I just had to do this. The old lines they used back then could not handle the ethanol. Half of the fuel line ended up in my carbs.

I just had this same problem with my '89 60hp Rude. This was my first boat that I had bought last October. Never ran right from the day I bought it. Took it to one mechanic who did the carbs and kits, lower unit and a lot of other stuff. When I got it back, it was still doing the same thing. Before I get into it, two things. Make sure your mechanic takes it to the lake and runs it in the water, not just on ear muffs. And tell him to make sure to quadruple check the new needle and seats in the carb kits!
First mechanic did the work, but it didn't fix the root of the problem. Second mechanic took the time to chase the ghosts and get down to what was wrong. Turns out I got an entire fuel system rebuild after all was said and done. He also took the time to SHOW me what the problems were. Like I stated earlier, the rubber tip on the needle valve in the new carb kit was revamped by the carb kit company, and did not seat properly in the assembly. Had to soak the old needles to soften the rubber, clean and reinstall. Had to compare the new needles tips with the old to find this problem. He also took it to the lake to test and learn what was going on with the fuel delivery, not just putting it on the earmuffs. In the end, all the fuel lines had to be replaced, the gas tank taken out and pressure washed, new fuel pump, reed cages repaired, just everything from top to bottom. Oh, and my voltage regulator had melted too for some reason or another. Don't know if it was like that when I got it or not. Figure the first mechanic would have at least noticed the goo running all over the wiring and block.
My motor was doing the exact same thing yours is. Ran fine when putting the juice to it, but getting there was a nightmare. It would not low idle when in gear, like when trying to load or in a no wake zone. I can't say enough good stuff about the mechanic who actually fixed the problem. Being this is my first boat, he took the time to explain problems and actually show me things. Excellent customer service. Even worked with me on the price. His name is Mike and it's Discount Maintenance Marine in Arlington. 817-274-1050

My 130 Johnson is having the same symptoms. I was going to rebuild the carbs this winter. Didn't know to check the fuel lines.

One thing not mentioned that I had trouble with on an older
motor with simular problems. Ended up being a problem in the
check valves of my squeeze bulb, you could pump gas into the
motor to start it but wouldn't keep the flow through the
bulb, so now I always check that first, as it is easy to replace
and not expensive. But as stated in the above answers, there is
a lot of small things that can cause the trouble.

Check your in line fuel filter

Give the boatwhisperer here on the forum a shout, he is a very good mechanic that special is older motors.Dennis @817-455-8377. he is in Hurst

Great. Thanks.